I have a gpg .key file that is used as passphrase for decrypting a .dat.pgp file. The encrypted .data.pgp file gets successfully decrypted on one server with same .key file
I just ran into this issue, on the gpg CLI in Arch Linux. I needed to kill the existing "gpg-agent" process, then everything was back to normal ( a new gpg-agent should auto-launch when you invoke the gpg command, again; ...).
gpg-agent in a terminal and/or reboot ...